How does a prism reflect light into the colors of
the rainbow? I know it uses refraction, but how
is it actually refracting the light through the
prism and seperating the colors from the white
light?

Answer 1:

Great question. I remember asking the same
question in school!

Let's start with
refraction. In a way, refraction simply means
that light travels at a different speed in
different materials. It's fast in air, and slower
in water or glass. This has the effect of
changing the direction of light, or bending it,
when it moves from one material to the other.
Here's one way to think about why it changes
direction. Let's say you're driving a Segway
along a road next to a thick, grassy field. And
say you can drive faster on the road than on the
grass. Now if one wheel drops off the road into
the grass, what happens? That wheel will suddenly
slow down, which will turn you toward the field
(assuming you don't steer to correct it). Once
both wheels are on the grass, you'll go straight
again--but away from the road. The transition
from the road to the grass made you take a turn.
The same is true of light moving from air (the
road) to glass (the grass).

But why do
different colors go in different directions? This
is because different colors of light travel at
*different speeds* in the glass. So from the
analogy above, slower speeds in the glass make the
light bend more. We call this effect dispersion,
since it disperses the colors in different
directions. Blue light travels slightly slower in
glass than red light, so it bends a sharper angle
when it enters the glass from air. In physics, we
say the glass has a higher refractive index for
blue light than red light. There is a formula
(Snell's Law) that you can use to calculate angles
from refractive index, or the other way around.

Answer 2:

When we send white light into a prism, we are
actually sending in a mixture of all colors. A
prism does not create colors from white light. As
you said, it just separates out the different
colors that are already there. The most accurate
scientific explanation for HOW refraction actually
works is a theory called quantum
electrodynamics.That theory is a difficult
subject, too detailed for me to explain here, but
maybe I can give you a feel for what happens in a
prism. The different colors of light all travel at
roughly the same speed in air. In glass, however,
this is not true. Blue light gets slowed down by
glass more than red light. As a result of their
different speeds in the glass, the red and blue
light get bent at different angles when they go
into the prism. This separates blue from red, and
in fact it separates all of the colors we can
see.

Perhaps you are wondering "So why do
different colors travel at different speeds in
glass?" It has to do with the way that light
interacts with atoms in the glass - that is what
quantum electrodynamics is all about, how light
interacts with atoms. There is a book called QED
by Richard Feynman that would probably be the best
place to start learning about quantum
electrodynamics if you are curious to learn more.
Most books about this subject require a lot of
studying and math, but this one is written for
people who are just curious but don't have the
time or patience to learn all the details.